Navigates through MaxL status messages one at a time.
Arguments: none.
Returns: a list of the form (<message_number>, <message_level>, <message_text>)
Each invocation of the "do" method results in a stack of status messages. This stack is unwound by repeatedly calling pop_msg until it returns nothing. It is acceptable for a Perl program to ignore the message stack or to unwind it only partially. The next call to "do" will clear left-over messages.
There will probably be a number of messages on the stack even after a successful execution. In most cases, a Perl program will only need to know if the execution of the last "do" was successful, which is indicated by the return value from "do".
When the message stack is empty, the return list elements are undfined and Essbase{STATUS} is set to $MAXL_STATUS{END_OF_DATA}.